1. Field of the Invention
The present invention relates to a method of folding an air bag in an air bag system disposed in a steering wheel of a car, or in an instrument panel in front of a passenger seat, or the like.
The present application is based on Japanese Patent Application No. Hei. 11-336717, which is incorporated herein by reference.
2. Description of the Related Art
An air bag system disposed in a steering wheel is hitherto known, for example, in JP-A-10-175494. Such an air bag is sewed, folded and received in a case as follows.
That is, a bottom wall portion provided with an inlet opening for introducing inflating gas and a ceiling wall portion opposite to the inlet opening are cut out into predetermined shapes respectively. Then, the bottom wall portion and the ceiling wall portion are put on each other so that the surfaces which will be the outer circumferential surface sides of the air bag face each other. The outer circumferential edges of the bottom wall portion and the ceiling wall portion are sewed with each other. Then, the sewed air bag is reversed through the inlet opening. The reason why the air bag is reversed in such a manner is that the margin to sew up the bottom wall portion and the ceiling wall portion is prevented from being exposed on the outer circumferential surface of the air bag.
After that, in the state where the bottom wall portion and the ceiling wall portion are put on each other so as to be unfolded flatly, the circumferential edge of the air bag is folded to come close to the inlet opening.
The air bag folded thus is attached to a bag holder of a case which is constituted by the bag holder and an air bag cover (pad), while the pad is connected to the bag holder. Thus, the air bag is received in the case.
Incidentally, in the aforementioned air bag system, an inflator for supplying inflating gas to the air bag is incorporated in the air bag at the same time as the air bag is received in the case. Thus, the assembling of the air bag system is completed. Then, by use of the case (bag holder), the air bag system is attached to a steering wheel body which is coupled with a steering shaft of a vehicle. Thus, the assembling and mounting of the steering wheel on the vehicle is completed.
However, in the background art, the air bag is folded after it is reversed through the inlet opening. When the air bag is passed through the inlet opening, the circumferential edge of the air bag is folded to come close to the inlet opening because the opening area of the inlet opening is smaller than the area of the flatly unfolded bottom wall portion or the flatly unfolded ceiling wall portion. Then, when the air bag is folded after it is reversed, the circumferential edge of the air bag is folded again in the state where the bottom wall portion and the ceiling wall portion are unfolded flatly. Therefore, the work of folding the air bag before reversing it is quite useless.
It is therefore an object of the present invention to solve the foregoing problem.
It is another object of the present invention to provide a method of folding an air bag in which the work of folding the air bag after sewing up it and before receiving it in a case can be performed efficiently with no waste, so that the air bag can be received in the case with a reduced number of man-hour for the work of folding.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a method of folding an air bag comprising: preparing a bottom wall portion with an inlet opening for introducing inflating gas, and a ceiling wall portion opposite to the inlet opening; sewing outer circumferential edges of the bottom wall portion and the ceiling wall portion with each other so as to form an air bag; pre-folding the sewed air bag to make a circumferential edge of the sewed air bag close to the inlet opening after the sewing and before reversing so that creases to be formed when the air bag is received in a case are formed partly in advance; reversing the pre-folded air bag through the inlet opening; further folding the reversed air bag so as to make the circumferential edge of the air bag close to the inlet opening; and putting the folded air bag into the case.
In the above method of folding an air bag, preferably, the pre-folding is carried out so that at least two creases are provided for making circumferential edges on opposite sides of the air bag close to the inlet opening respectively.
In the above method.of folding an air bag, preferably, the pre-folding is carried out by inward-roll-folding in which the circumferential edges of the air bag are rolled toward the ceiling wall portion.
In the above method of folding an air bag, preferably, when the air bag having a tether with at least two foot portions for connecting the bottom wall portion and the ceiling wall portion with each other, in the pre-folding operation, circumferential edges on opposite sides of the air bag where the two foot portions are disposed are folded to come close to the inlet opening so as to be enveloped by the two foot portions.
In the method of folding an air bag according to the present invention, before the air bag is reversed and after the outer circumferential edges of the bottom wall portion and the ceiling wall portion are sewed with each other, pre-folding is performed to make the circumferential edge of the air bag close to the inlet opening so as to form in advance a part of crease. The crease will be formed when the air bag is received in the case. Then, the air bag is reversed through the inlet opening. After being reversed, the air bag is folded after the pre-folding.
That is, folding after the air bag is reversed can be performed without any work of releasing the folding to thereby unfold the air bag flatly as in background art, because pre-folding is performed before the air bag is reversed. Thus, the folding after the air bag is reversed can be simplified. In addition, the pre-folding itself can make the air bag compact before the air bag is passed through the inlet opening. Accordingly, the background-art useless folding work before the air bag is passed through the inlet opening can be reduced to the utmost.
In addition, the air bag which has been reversed is compact because the air bag is pre-folded. Therefore, the space for the work of folding thereafter can be reduced so that a folding machine can be also miniaturized.
Accordingly, in the method of folding an air bag according to the present invention, the work of folding the air bag after sewing it up and before receiving it in the case can be performed efficiently with no waste, so that the air bag can be received in the case with a reduced number of man-hour for the work of folding. Further, the work of folding the air bag after reversing it can be performed in a saved space.
The pre-folding may be carried out so that at least two creases are provided for making the circumferential edges on opposite sides of the air bag close to the inlet opening respectively. In this case, in the air bag which has been folded up, the creases formed in the pre-folding operation are rolled in the air bag so as to intrude into the air bag. As a result, the resistance to releasing the pre-folding is increased when the air bag is unfolded and inflated, and the opposite sides of the air bag which have not been pre-folded are unfolded quickly. When the folded air bag is disposed in a boss portion of a steering wheel, the portions of the air bag which will be disposed on the left and right sides of the steering wheel are pre-folded with at least two creases respectively. Thus, the air bag is inflated easily in the front/rear direction when the air bag is unfolded and inflated. Accordingly, interference in the left and right arms of a driver can be prevented in the unfolding and inflating operation of the air bag.
Further, if the pre-folding is carried out by inward-roll-folding on the ceiling wall portion side, the resistance to releasing the inward-roll-folding is large when the air bag is unfolded and inflated. When the folded air bag is disposed in a boss portion of a steering wheel, the portions of the air bag which will be disposed on the left and right sides of the steering wheel are inward-roll-folded with at least two creases respectively. As a result, when the air bag is unfolded and inflated, it is further prevented from being unfolded in the left/right direction, but is inflated easily in the front/rear direction. Accordingly, interference in the left and right arms of a driver can be further prevented in the unfolding and inflating operation of the air bag.
Moreover, in the case where the air bag has a tether with at least two foot portions, in the pre-folding operation, the circumferential edges on opposite sides of the air bag where the two foot portions are disposed may be folded to come close to the inlet opening so as to be enveloped by the two foot portions. In this case, because the two foot portions of the tether envelop the folded portions, the creases formed in the pre-folding operation are difficult to be released. The work of reversing the air bag through the inlet opening can be carried out smoothly while the creases are prevented from being released. In addition, it becomes easy to keep the compact shape of the air bag after the work of reversing.